The principle of operation of such a field device is that the oscillation of an oscillatable unit depends on whether it is oscillating freely or covered by the medium—this is then the fill level determination—or whether, for example, the viscosity of the medium changes—this is then e.g. the monitoring of viscosity. Depending on a property of the medium, or, in general, whether the medium is covering the oscillatable unit, or not, the frequencies and amplitudes of the oscillations will differ. Working backwards from a frequency change, thus, allows, for example, in the case of application as a fill-level sensor, the conclusion that the medium has exceeded, or subceeded (or fallen beneath), a certain fill level, as determined by the installed position of the sensor. The same holds also for the amplitude.
The assignee manufactures and sells oscillating forks under the mark LIQUIPHANT, e.g. for fill level detection. The advantage of oscillating forks lies in the fact that the oscillations of the two fork tines exactly compensate, or cancel, so that e.g. no energy of the fork is transferred to the region of attachment, thus to the area where the measuring device is connected to the container, and, from there, into the container itself. For types of application in which it is possible, for example, that material can get stuck between the tines, it is of interest to use so-called single-rod devices. In this case, the inherent canceling of the forces is lacking, and, consequently, forces and torques can act on the attachment.